The material for the binder 105 may include a water-soluble polymer such as polyvinyl alcohol, water-soluble ethylene-vinyl alcohol copolymer, polyvinyl butyral, polyethylene glycol, sodium carboxymethyl cellulose and hydroxyethyl cellulose; a fluororesin such as polyvinylidene fluoride and vinylidene fluoride-hexafluoropropylene copolymer; a polyolefin such as polyethylene and polypropylene; styr